1. Field of the Invention
The present invention relates to a non-contact IC card capable of non-contact data communication with readers/writers.
2. Description of the Related Art
Recently, a variety of services using various communication technologies, such as electronic commerce or on-line shopping over the Internet or the like, have become popular. With the growth of communication technologies, terminal-based communication systems and card-like devices including non-contact semiconductor memory cards having a communication function integrated into a circuit (these devices are hereinafter referred to as non-contact IC (integrated circuit) cards) have been developed for use in various situations such as electronic toll collection of transportation facilities and electronic money transactions. In view of their convenience of handling, the non-contact IC cards must have a reduced circuit size and operate with very low power consumption.
The services using such non-contact IC cards generally require mutual authentication to authenticate the communicating parties and encryption to ensure data communication security. These functions must be performed at high speed in the non-contact IC cards. These functions, which are implemented by software, require a high-clock CPU (central processing unit), which is not suitable for practical use. Therefore, it is desirable that the mutual authentication function and the encryption function be implemented in the non-contact IC cards by hardware rather than software.
Most of the non-contact IC cards in which these functions are implemented by hardware employ so-called common key encryption algorithms, e.g., DES (data encryption standard), to reduce the consumption power because relatively reduced circuit size and power consumption of the non-contact IC cards are achievable. Some of the non-contact IC cards which employ the common key encryption algorithms typically have a communication distance of several centimeters to a reader/writer. Even a communication distance of as much as 10 cm can be realized, depending upon the type of interface.
However, in the common key encryption algorithms, a common key is used for both encoding and decoding, and so transmission and reception of key data are essential. Therefore, the common key encryption algorithms are vulnerable to attacks from unauthorized third parties. This has led to fears that the non-contact IC cards applied to financial services in the future may have problems.
In the services using non-contact IC cards, therefore, the demands for high security systems using so-called public key encryption algorithms, e.g., RSA (Rivest-Shamir-Adleman) and ECC (elliptic curve cryptosystem), have increased. In public key encryption, separate keys are used for encoding and decoding and a secret common key is kept by one particular individual. Many studies on non-contact IC cards for performing signature generation and authentication using public key techniques have been made.
Public key encryption algorithms have higher security than common key encryption algorithms, but require a large amount of calculation. Public key encryption algorithms implemented by hardware require circuits several tens of times larger than otherwise and also require a large amount of power supplied to such large circuits.
In the art, non-contact IC cards using the public key encryption algorithms have not achieved the desired characteristics in terms of circuit size, power consumption, and cost. In the current non-contact IC cards, most of the power must be supplied to an encryption circuit, and the communication distance is as small as about several millimeters.
Although the demands for non-contact IC cards using public key encryption algorithms having high security robustness have increased, it is difficult to implement the algorithms because such non-contact IC cards have limitations on power supply, chip size, etc., and the small communication distance is not suitable for practical use.